It is known that the detection of delayed sensitivity reactions which are the basis for cutaneous testing for tuberculosis can be accomplished by a material extracted from Mycobacterium bovis, strain BCG (Bacillus Calmette-Guerin). This BCG derived material, as well as so-called old tuberculin (O.T.) and Purified PROTEIN Derivative (PPD) are heterogeneous in composition. There is, consequently, a need for a purer and more precisely characterized antigenic material, possessing greater and more reliable effectiveness for the cutaneous testing for such diseases.
It was found that a high molecular weight antigenic material related in important immunochemical respects to the A60 antigen of M. bovis strain BCG may be extracted from various Mycobacterial species in substantially immunochemically pure form by the method claimed in U.S. patent application No. 678,170, filed Dec. 5, 1984. This antigenic material proved to possess those properties required to serve as the capture antigen in diagnostic test procedures and resulted in the development of an effective serological diagnostic test also claimed in that application. Taking advantage of the refined and reliable detection test thus made available, it has now been established that the A60 like antigenic material in question can be effectively used as the challenge antigen in delayed sensitivity tests for confirming the acquisition of immunity upon vaccination as well as prior exposure of the subject to tubercular-related infections.